Microwave interactive flexible packaging

ABSTRACT

A package configured to receive a food item for storage and heating therein is disclosed. The package includes an opening and a closure mechanism and comprises an insulating microwave material. A plurality of packages in a stacked relation also is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/096,440, filed Apr. 1, 2005, now U.S. Pat. No. 7,323,669 which is acontinuation-in-part of U.S. patent application Ser. No. 10/501,003filed Mar. 7, 2005, now U.S. Pat. No. 7,019,271, issued Mar. 28, 2006,which is the National Stage of International Application No.PCT/US03/03779, filed Feb. 7, 2003, which claims the benefit of U.S.Provisional Application No. 60/355,149, filed Feb. 8, 2002; and is alsoa continuation-in-part of U.S. patent application Ser. No. 11/054,633filed Feb. 9, 2005, now U.S. Pat. No. 7,365,292 which claims the benefitof U.S. Provisional Application No. 60/543,364 filed Feb. 9, 2004. Theabove-referenced applications each are incorporated by reference hereinin their entirety.

TECHNICAL FIELD

The present invention relates to packages for heating or cooking a fooditem. In particular, the invention relates to a package for heating orcooking a food item in a microwave oven.

BACKGROUND

Microwave ovens provide a convenient means of cooking and reheating fooditems. Frequently, users transport microwaveable food items from home towork or another location by placing the food item in a plastic bag,aluminum foil, plastic wrap, or a plastic container. Although some ofsuch materials or containers may be placed in the microwave oven, suchmaterials or containers often result in the food item being undesirablysoggy. In contrast, by merely cooking the food item on a paper plate,napkin, paper towel, or other commonly available substrate, the fooditem often becomes dried out and hardened.

Many combinations of materials of different character have been used inmicrowave packaging to influence the effect of the microwave energy onthe food product being heated. These microwave packaging materials maybe microwave transparent, for example, paper, paperboard, or manyplastics, or they may be microwave interactive, for example, metal foilsor thin metal deposits. Microwave transparent materials generallyprovide, for example, food product support, packaging form, insulation,and vapor barrier functions in packaging. Microwave interactivematerials generally provide, for example, enhanced surface heating,microwave shielding, enhanced microwave transmission, and energydistribution functions in packaging. Microwave packaging often iscreated and configured for a particular food product or type of foodproduct using materials chosen to best exploit the cooking ability of amicrowave oven with respect to that food product. However, suchpackaging typically is provided only with the particular food item andis not independently available for purchase and use with food itemsprepared by a user.

Thus, there is a need for a package for a food item that may be used tocontain a food item, transport the item between locations, and heat orcook the food product therein. Further, there is a need for a packagethat provides browning and/or crisping of the food item during microwaveheating or cooking. Still further, there is a need for a package that isavailable for purchase and use with food items prepared by a user.

SUMMARY

The present invention relates generally to a package that can be usedfor storing, transporting, and heating a food item therein. The packageis formed at least partially from at least one material that enhancesheating in a microwave oven.

In one aspect, the present invention is directed to a package forreceiving a food item for storage and heating therein. The packagecomprises at least one opening, at least one mechanism for closing theat least one opening, and an insulating microwave material. The packageincludes an interior into which the food item is placed, and an interiorsurface on which the food is supported. The package further may includeat least one vent to permit the passage of water vapor therefrom. Thevent may be an aperture, perforation, or other suitable feature or,alternatively, may be a closure mechanism that is sealed only partiallyduring heating, thereby permitting water vapor to escape.

In this and other aspects of the present invention, the closuremechanism may be any suitable mechanism as desired. For example, theinterior surface of the package proximate the opening may include anadhesive material covering at least a portion thereof. Alternatively,the closure mechanism may be a zipper or slider-type closure.Alternatively still, the closure mechanism may include a flap extendingfrom an open end of the package, where the flap is adapted to beinserted into the opening.

In yet another alternative, the closure mechanism may include a flapextending from an open end of the package, where the flap includes amechanism for releasably sealing the package. In one aspect, themechanism for releasably sealing the package may include an adhesivematerial covering at least a portion of the flap, where, for example,the flap is adapted to be folded over the opening such that the adhesivecontacts an exterior surface of the package. In another aspect, themechanism for releasably sealing the package may include a tab extendingfrom the flap that communicates with a corresponding slot in thepackage.

In another aspect, the present invention is directed to a package forheating a food product comprising a sleeve formed at least partiallyfrom an insulating microwave material and having at least two open ends,where the sleeve has an interior surface comprising an adhesive coveringat least a portion thereof for substantially sealing the package. In oneaspect, the insulating microwave material comprises expandableinsulating cells. In another aspect, the insulating microwave materialcomprises a susceptor material.

In yet another aspect, the present invention is directed to a packagefor storing and heating a food item therein, where the package is formedat least partially from an insulating material including a barrier film.The package comprises an opening through which the food item is receivedand a closure mechanism proximate the opening for substantially sealingthe package. The barrier film may comprise ethylene vinyl alcohol,barrier nylon, polyvinylidene chloride, barrier fluoropolymer, nylon 6,nylon 66, coextruded nylon 6/ethylene vinyl alcohol/nylon 6, siliconoxide coated film, or any combination thereof. In one aspect, thebarrier film has an oxygen transmission rate of less than about 80cc/m²/day. In another aspect, the barrier film has an oxygentransmission rate of less than about 25 cc/m²/day. In yet anotheraspect, the barrier film has a water vapor transmission rate of lessthan about 450 g/m²/day.

In this and other aspects, the present invention contemplates aplurality of packages stacked in a face-to-face relation. The pluralityof packages may be placed into a carton comprising an open portionthrough which the microwave cooking packages may be removed ordispensed.

Other aspects, features, and advantages of the present invention willbecome apparent from the following description and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary package according to the present invention,in the form of a sleeve;

FIG. 2 is a cross-sectional view of the package of FIG. 1 with a fooditem contained therein;

FIG. 3 depicts another exemplary package according to the presentinvention, in the form of a sleeve;

FIG. 4 is a cross-sectional view of the package of FIG. 3 with a fooditem contained therein;

FIG. 5 depicts another exemplary package according to the presentinvention, in the form of a sleeve;

FIG. 6 is a cross-sectional view of the package of FIG. 5 with a fooditem contained therein;

FIG. 7 depicts another exemplary package according to the presentinvention, in the form of a sleeve, in an open configuration;

FIG. 8 depicts the package of FIG. 7 in a closed configuration;

FIG. 9 depicts an exemplary package according to the present invention,in the form of a pouch;

FIG. 10 depicts another exemplary package according to the presentinvention, in the form of a pouch;

FIG. 11 depicts another exemplary package according to the presentinvention, in the form of a pouch;

FIG. 12 depicts another exemplary package according to the presentinvention, in the form of a pouch;

FIG. 13 depicts another exemplary package according to the presentinvention, in the form of a pouch;

FIG. 14 depicts another exemplary package according to the presentinvention, in the form of a pouch;

FIG. 15 is a cross-sectional view of an insulating microwave materialthat may be used in accordance with the present invention;

FIG. 16 is a cross-sectional view of an alternative insulating microwavematerial that may be used in accordance with the present invention;

FIG. 17 is a perspective view of the insulating microwave material ofFIG. 15;

FIG. 18 depicts the insulating microwave material of FIG. 17 afterexposure to microwave energy;

FIG. 19 is a cross-sectional view of yet another insulating microwavematerial that may be used in accordance with the present invention;

FIG. 20 is a cross-sectional view of still another insulating microwavematerial that may be used in accordance with the present invention;

FIG. 21 depicts the package of FIG. 1 formed from an insulatingmicrowave material, after exposure to microwave energy;

FIG. 22 depicts the package of FIG. 9 formed from an insulatingmicrowave material, after exposure to microwave energy; and

FIG. 23 depicts the package of FIG. 10 formed from an insulatingmicrowave material, after exposure to microwave energy.

DESCRIPTION

The present invention generally is directed to a disposable package forstoring a food item, and browning and crisping the food item in amicrowave oven. The package may be provided as a sleeve, a pouch, a bag,or any other configuration as desired. Unlike conventional sandwichbags, plastic containers, and the like, the package of the presentinvention includes features that store the item during transportationand brown and crisp the food item during the heating or cooking cycle inthe microwave oven.

The sleeve or pouch may be provided with one or more features that allowthe bag to be sealed during refrigeration, freezing, transportation,heating, or otherwise. In one aspect, the sleeve or pouch is providedwith one or more strips of pressure-sensitive adhesive near theperiphery thereof so that, after the food item is positioned, thepackage may be sealed around the edges of the food item. In anotheraspect, the sleeve or pouch is provided with an open portion forinserting the food item therein, and a flap adjacent thereto. The flapmay be folded over to close the end and may be inserted into a slot tosecure the food item therein. In yet another aspect, the flap isprovided with an adhesive that secures the package when brought intocontact with an exterior surface of the package. If desired, the featurefor closing the package may be selected to substantially seal thepackage for protection of the food item during storage in a refrigeratoror freezer, or to store or transport a food item that has a liquidcomponent or other components that might tend to fall out of thepackage.

In any of the packages contemplated hereby, the sleeve or pouch mayinclude one or more venting mechanisms. For example, the package may beprovided with apertures or perforations that permit vapor to escapeduring cooking. Alternatively, the package may be re-opened partially orcompletely at one or more ends, edges, or locations to provide ventingof the food product.

The present invention may be best understood by referring to thefollowing figures. For purposes of simplicity, like numerals may be usedto describe like features. However, it should be understood use of likenumerals is not to be construed as an acknowledgement or admission thatsuch features are equivalent in any manner.

FIGS. 1-14 depict several exemplary packages that may be formedaccording to the present invention. The exemplary packages have a sleeveor pouch configuration and are shown to be hand-held type packages.However, it should be understood that other shapes and configurationsare contemplated by the present invention. Examples of other shapesencompassed hereby include, but are not limited to, polygons, circles,ovals, cylinders, prisms, spheres, polyhedrons, ellipsoids, and anyother shape that may be formed into a three-dimensional package forreceiving a food item therein. The shape of the package may bedetermined by the shape of the food product intended for use therewith,and it should be understood that different packages are contemplated fordifferent food products, for example, sandwiches, corn dogs, pizzas,French fries, soft pretzels, pizza bites, cheese sticks, pastries,doughs, and so forth. Additionally, it should be understood that thepresent invention contemplates packages for single-serving portions andfor multiple-serving portions, and is not restricted to hand-heldpackages. It also should be understood that various components used toform the packages of the present invention may be interchanged. Thus,while only certain combinations are illustrated herein, numerous othercombinations and configurations are contemplated hereby.

According to one aspect of the present invention shown in FIGS. 1 and 2,the package comprises a sleeve 100 having an interior 110, an exteriorsurface 115, an open first end 120, and an open second end 125 (shown indashed lines). Various closure mechanisms may be provided to seal thepackage for refrigeration, freezing, or transportation. For example, anadhesive strip 130 may be provided on the interior surface 135 of thesleeve 100 proximate the first end 120 and the second end 125. Anysuitable adhesive may be used, and in some instances, the adhesive is apressure-sensitive adhesive. As shown in FIG. 2, after the food item Fis placed into the sleeve 100, the respective ends 120, 125 of thesleeve 100 may be pressed together to seal the food item F therein. Ifdesired, the adhesive may be covered with a removable release liner,such as those known in the art.

Alternatively, as shown in FIGS. 3 and 4, the first end 155 and secondend 160 of the sleeve 150 may include flaps 165, 170 that fold into theinterior 175 of the sleeve 150 to enclose the food item F therein.Alternatively still, as shown in FIGS. 5 and 6, the flaps 165, 170 mayinclude adhesive strips 172, 174 that are pressed against the exterior176 of the package 150 to enclose the food product F therein. In anotherexample shown in FIGS. 7 and 8, the flaps 165, 170 may include tabs 180,185 or other projections that are inserted into corresponding slots 190,195 in the sleeve 150. While various enclosure mechanisms are providedherein, it should be understood that the present invention contemplatesnumerous other closure mechanisms.

According to another aspect of the present invention shown in FIG. 9,the package comprises a pouch 200 having an interior 205, an exteriorsurface 210, a plurality of sealed edges 215 a, 215 b, and 215 c, and atleast one open end 220 or open portion. The pouch 200 may be shaped andsized to receive one or more food items (not shown). For example, asshown in FIG. 10, the pouch 200 may be somewhat rectangular in shape andmay include one or more gussets 225 as needed to accommodate larger orthicker food items (not shown), for example, one or more pieces of friedchicken. As shown in FIG. 11, the pouch 200 may be elongated in shape toaccommodate, for example, a submarine sandwich, an egg roll, or burrito.As shown in FIG. 12, the pouch 200 may be triangular in shape toaccommodate, for example, a slice of pizza. As shown in FIG. 13, thepouch 200 may be substantially square in shape to accommodate, forexample, a sandwich, such as a grilled cheese sandwich or a meat andcheese sandwich. As shown in FIG. 14, the pouch 200 may be circular orrounded in shape to accommodate, for example, a pot pie.

In each of the exemplary packages shown in FIGS. 9-14, various closuremechanisms may be provided. For example, any of the closure mechanismsshown in or described in connection with FIGS. 1-8 may be used,including one or more adhesives strips (FIGS. 1, 2, 5, 6), flaps (FIGS.3, 4, 5, 6), tabs (FIGS. 7, 8), zippers, which typically comprise atleast one elongated ridge and at least one mating and releasablyinterlocking elongated groove (FIG. 14), sliders, which are zipper-typefasteners that typically include a sliding bar that causes the ridge(s)to engage with the groove(s) as the slider is moved along the opening(FIG. 13), or the like, or any combination thereof, as are known tothose of skill in the art. Other closure mechanisms are contemplatedhereby.

Any of the numerous packages contemplated hereby may be formed from oneor more microwave energy interactive materials that promote browningand/or crisping of the food item during microwave heating. In oneaspect, the package may include one or more susceptor materials. Thesusceptor material may form all or part of the package as needed ordesired to brown or crisp the food item. Thus, for instance, where thepackage is intended for use with a slice of pizza, the susceptormaterial may form all or part of the portion of the package in contactwith or proximate the crust of the pizza. As another example, where thepackage is intended for a sandwich or a burrito, substantially all ofthe interior surface of the package may be provided with a susceptormaterial.

A susceptor used in accordance with the present invention may comprise amicrowave energy interactive material deposited on or supported by asubstrate. Depending on the microwave energy interactive materialselected and its positioning in the packaging, the susceptor may absorbmicrowave energy, transmit microwave energy, or reflect microwave energyas desired for a particular food product. When the food product isplaced inside the package, the microwave energy interactive material maybe in proximate contact with the surface of the food product, intimatecontact with the food product, or a combination thereof, as needed toachieve the desired cooking results.

The microwave energy interactive material may comprise anelectroconductive or semiconductive material. According to one aspect ofthe present invention, the microwave energy interactive material maycomprise a metal or a metal alloy provided as a metal foil; a vacuumdeposited metal or metal alloy; or a metallic ink, an organic ink, aninorganic ink, a metallic paste, an organic paste, an inorganic paste,or any combination thereof. Examples of metals and metal alloys that maybe suitable for use with the present invention include, but are notlimited to, aluminum, chromium, copper, inconel alloys(nickel-chromium-molybdenum alloy with niobium), iron, magnesium,nickel, stainless steel, tin, titanium, tungsten, and any combinationthereof.

While metals are inexpensive and easy to obtain in both vacuum depositedor foil forms, metals may not be suitable for every application. Forexample, in high vacuum deposited thickness and in foil form, metals areopaque to visible light and may not be suitable for forming a clearmicrowave package or component. Further, the interactive properties ofsuch vacuum deposited metals for heating often are limited to heatingfor narrow ranges of heat flux and temperature. Such materials thereforemay not be optimal for heating, browning, and crisping all foodproducts. Additionally, for field management uses, metal foils andvacuum deposited coatings can be difficult to handle and design intopackages, and can lead to arcing at small defects in the structure.

Thus, according to another aspect of the present invention, themicrowave interactive energy material may comprise a metal oxide.Examples of metal oxides that may be suitable for use with the presentinvention include, but are not limited to, oxides of aluminum, iron, andtin, used in conjunction with an electrically conductive material whereneeded. Another example of a metal oxide that may be suitable for usewith the present invention is indium tin oxide (ITO). ITO can be used asa microwave energy interactive material to provide a heating effect, ashielding effect, or a combination thereof. To form the susceptor, ITOtypically is sputtered onto a clear polymeric film. The sputteringprocess typically occurs at a lower temperature than the evaporativedeposition process used for metal deposition. ITO has a more uniformcrystal structure and, therefore, is clear at most coating thicknesses.Additionally, ITO can be used for either heating or field managementeffects. ITO also may have fewer defects than metals, thereby makingthick coatings of ITO more suitable for field management than thickcoatings of metals, such as aluminum.

Alternatively, the microwave energy interactive material may comprise asuitable electroconductive, semiconductive, or non-conductive artificialdielectric or ferroelectric. Artificial dielectrics comprise conductive,subdivided material in a polymeric or other suitable matrix or binder,and may include flakes of an electroconductive metal, for example,aluminum.

The substrate used in accordance with the present invention typicallycomprises an electrical insulator, for example, a polymeric film. Thethickness of the film may typically be from about 35 gauge to about 10mil. In one aspect, the thickness of the film is from about 40 to about80 gauge. In another aspect, the thickness of the film is from about 45to about 50 gauge. In still another aspect, the thickness of the film isabout 48 gauge. Examples of polymeric films that may be suitableinclude, but are not limited to, polyolefins, polyesters, polyamides,polyimides, polysulfones, polyether ketones, cellophanes, or anycombination thereof. Other non-conducting substrate materials such aspaper and paper laminates, metal oxides, silicates, cellulosics, or anycombination thereof, also may be used.

According to one aspect of the present invention, the polymeric film maycomprise polyethylene terephthalate. Examples of polyethyleneterephthalate film that may be suitable for use as the substrateinclude, but are not limited to, MELINEX®, commercially available fromDuPont Teijan Films (Hopewell, Va.), and SKYROL, commercially availablefrom SKC, Inc. (Covington, Ga.). Polyethylene terephthalate films areused in commercially available susceptors, for example, the QWIK WAVE®Focus susceptor and the MICRO-RITE® susceptor, both available fromGraphic Packaging International (Marietta, Ga.).

According to another aspect of the present invention, the package may beconstructed from materials that provide a water barrier, oxygen barrier,or a combination thereof to the susceptor. Such barrier layers may beformed from a polymer film having barrier properties or from any otherbarrier layer or coating as desired. Suitable polymer films may include,but are not limited to, ethylene vinyl alcohol, barrier nylon,polyvinylidene chloride, barrier fluoropolymer, nylon 6, nylon 66,coextruded nylon 6/EVOH/nylon 6, silicon oxide coated film, or anycombination thereof.

One example of a barrier film that may be suitable for use with thepresent invention is CAPRAN® EMBLEM 1200M nylon 6, commerciallyavailable from Honeywell International (Pottsville, Pa.). Anotherexample of a barrier film that may be suitable is CAPRAN® OXYSHIELD OBSmonoaxially oriented coextruded nylon 6/ethylene vinyl alcohol(EVOH)/nylon 6, also commercially available from HoneywellInternational. Yet another example of a barrier film that may besuitable for use with the present invention is DARTEK® N-201 nylon 66,commercially available from Enhance Packaging Technologies (Webster,N.Y.).

Still other barrier films include silicon oxide coated films, such asthose available from Sheldahl Films (Northfield, Minn.). Thus, in oneaspect, a susceptor may have a structure including a film, for example,polyethylene terephthalate, with a layer of silicon oxide coated ontothe film, and ITO or other material deposited over the silicon oxide. Ifneeded or desired, additional layers or coatings may be provided toshield the individual layers from damage during processing.

The barrier film may have an oxygen transmission rate (OTR) as measuredusing ASTM D3985 of less than about 20 cc/m²/day. In one aspect, thebarrier film has an OTR of less than about 10 cc/m²/day. In anotheraspect, the barrier film has an OTR of less than about 1 cc/m²/day. Instill another aspect, the barrier film has an OTR of less than about 0.5cc/m²/day. In yet another aspect, the barrier film has an OTR of lessthan about 0.1 cc/m²/day.

The barrier film may have an water vapor transmission rate (WVTR) asmeasured using ASTM F 1249 of less than about 100 g/m²/day. In oneaspect, the barrier film has a WVTR of less than about 50 g/m²/day. Inanother aspect, the barrier film has a WVTR of less than about 15g/m²/day. In yet another aspect, the barrier film has a WVTR of lessthan about 1 g/m²/day. In still another aspect, the barrier film has aWVTR of less than about 0.1 g/m²/day. In a still further aspect, thebarrier film has a WVTR of less than about 0.05 g/m²/day.

The microwave energy interactive material may be applied to thesubstrate in any suitable manner, and in some instances, the microwaveenergy interactive material is printed on, extruded onto, sputteredonto, evaporated on, or laminated to the substrate. The microwave energyinteractive material may be applied to the substrate in any pattern, andusing any technique, to achieve the desired heating effect of the foodproduct. For example, the microwave energy interactive material may beprovided as a continuous or discontinuous layer or coating, circles,loops, hexagons, islands, squares, rectangles, octagons, and so forth.Examples of alternative patterns and methods that may be suitable foruse with the present invention are provided in U.S. Pat. Nos. 6,765,182;6,717,121; 6,677,563; 6,552,315; 6,455,827; 6,433,322; 6,414,290;6,251,451; 6,204,492; 6,150,646; 6,114,679; 5,800,724; 5,759,422;5,672,407; 5,628,921; 5,519,195; 5,424,517; 5,410,135; 5,354,973;5,340,436; 5,266,386; 5,260,537; 5,221,419; 5,213,902; 5,117,078;5,039,364; 4,963,424; 4,936,935; 4,890,439; and 4,775,771; each of whichis incorporated by reference herein in its entirety. Although particularexamples of the microwave energy interactive material are shown anddescribed herein, it should be understood that other patterns ofmicrowave energy interactive material are contemplated by the presentinvention.

According to yet another aspect of the present invention, the susceptoroptionally is laminated to a support. The support may form a partial orcomplete layer of the susceptor. The support may be formed from paper,paperboard, a low shrink polymer, or any other suitable material. Thus,for example, a metallized polymer film may be laminated to a paper, forexample, a kraft paper, or alternatively, a low shrink polymer film, forexample, a cast nylon 6 or nylon 6,6 film, or a coextruded filmcontaining such polymers. One such material that may be suitable for usewith the present invention is DARTEK, commercially available from DuPontCanada.

Where the support is paper, the paper may have a basis weight of about15 to about 80 lbs/ream. In one aspect, the paper support has a basisweight of about 20 to about 60 lbs/ream. In another aspect, the papersupport has a basis weight of about 25 lbs/ream. Where the support ispaperboard, the support may have a thickness of about 8 to about 28mils. In one aspect, the paperboard support has a thickness of about 10to about 20 mils. In another aspect, the paperboard support has athickness of about 13 mils.

If desired, the support may be coated or laminated with other materialsto impart other properties, such as absorbency, repellency, opacity,color, printability, stiffness, or cushioning. Absorbent susceptors aredescribed in U.S. Provisional Patent Application Ser. No. 60/604,637,filed Aug. 25, 2004, incorporated herein by reference in its entirety.Additionally, the support may include graphics or indicia printedthereon. Where no additional support is present, the insulating materialmay act as a support for the susceptor, may be in direct contact withthe susceptor, and/or may be affixed thereto thermally, adhesively,mechanically, or any combination thereof, as is shown and describedherein.

In another aspect of the present invention, the package includes aninsulating microwave material. As used herein, an “insulating microwavematerial” refers to any arrangement of layers, such as polyester layers,susceptor layers, polymer layers, paper layers, continuous anddiscontinuous adhesive layers, and patterned adhesive layers thatprovide an insulating effect. The package may include one or moresusceptors, one or more expandable insulating cells, or a combination ofsusceptors and expandable insulating cells. Examples of materials thatmay be suitable, alone or in combination, include, but are not limitedto, are QwikWave® Susceptor packaging material, QwikWave® Focuspackaging material, Micro-Rite® packaging material, MicroFlex® Qpackaging material, and QuiltWave™ Susceptor packaging material, each ofwhich is commercially available from Graphic Packaging International,Inc. Any of such materials or other insulating materials may be used toform all or a portion of the packages shown in FIGS. 1-14 and FIGS.21-23 or contemplated hereby.

In one aspect of the present invention, the insulating microwavematerial includes at least one susceptor. By using an insulatingmicrowave material with a susceptor, more of the sensible heat generatedby the susceptor is transferred to the surface of the food productrather than to the microwave oven environment. Without the insulatingmaterial, some or all the heat generated by the susceptor may be lostvia conduction to the surrounding air and other conductive media, suchas the microwave oven floor or turntable. Thus, more of the sensibleheat generated by the susceptor is directed to the food product andbrowning and crisping is enhanced. Furthermore, insulating microwavematerials may retain moisture in the food item when cooking in themicrowave oven, thereby improving the texture and flavor of the fooditem.

Various exemplary insulating materials are depicted in FIGS. 15-20. Ineach of the examples shown herein, it should be understood that thelayer widths are not necessarily shown to scale. In some instances, forexample, the adhesive layers may be very thin with respect to otherlayers, but are nonetheless shown with some thickness for purposes ofclearly illustrating the arrangement of layers.

Referring to FIG. 15, the material 300 may be a combination of severaldifferent layers. A susceptor, which typically includes a thin layer ofmicrowave interactive material 305 on a first plastic film 310, isbonded for example, by lamination with an adhesive 312, to adimensionally stable substrate 315, for example, paper. The substrate315 is bonded to a second plastic film 320 using a patterned adhesive325 or other material, such that closed cells 330 are formed in thematerial 300. The closed cells 330 (shown unexpanded) are substantiallyresistant to vapor migration.

Optionally, an additional substrate layer 335 may be adhered by adhesive340 or otherwise to the first plastic film 310 opposite the microwaveinteractive material 305, as depicted in FIG. 16. The additionalsubstrate layer 335 may be a layer of paper or any other suitablematerial, and may be provided to shield the food item (not shown) fromany flakes of susceptor film that craze and peel away from the substrateduring heating. The insulating material 300 provides a substantiallyflat, multi-layered sheet 350, as shown in FIG. 17.

FIG. 18 depicts the exemplary insulating material 350 of FIG. 17 afterbeing exposed to microwave energy from a microwave oven (not shown). Asthe susceptor heats upon impingement by microwave energy, water vaporand other gases normally held in the substrate 315, for example, paper,and any air trapped in the thin space between the second plastic film320 and the substrate 315 in the closed cells 330, expand. The expansionof water vapor and air in the closed cells 330 applies pressure on thesusceptor film 310 and the substrate 315 on one side and the secondplastic film 320 on the other side of the closed cells 330. Each side ofthe material 300 forming the closed cells 330 reacts simultaneously, butuniquely, to the heating and vapor expansion. The cells 330 expand orinflate to form a quilted top surface 360 of cells separated by channelsin the susceptor film 310 and substrate 315 lamination, which loftsabove a bottom surface 365 formed by the second plastic film 320. Thisexpansion may occur within 1 to 15 seconds in an energized microwaveoven, and in some instances, may occur within 2 to 10 seconds.

FIGS. 19 and 20 depict alternative exemplary microwave insulatingmaterial layer configurations that may be suitable for use with any ofthe various packages of the present invention. Referring first to FIG.19, an insulating microwave material 400 is shown with two symmetricallayer arrangements adhered together by a patterned adhesive layer. Thefirst symmetrical layer arrangement, beginning at the top of the figure,comprises a PET film layer 405, a metal layer 410, an adhesive layer415, and a paper or paperboard layer 420. The metal layer 410 maycomprise a metal, such as aluminum, deposited along a portion or theentire PET film layer 405. The PET film 405 and metal layer 410 togetherdefine a susceptor. The adhesive layer 415 bonds the PET film 405 andthe metal layer 410 to the paperboard layer 420.

The second symmetrical layer arrangement, beginning at the bottom of thedrawings, also comprises a PET film layer 425, a metal layer 430, anadhesive layer 435, and a paper or paperboard layer 440. If desired, thetwo symmetrical arrangements may be formed by folding one layerarrangement onto itself. The layers of the second symmetrical layerarrangement are bonded together in a similar manner as the layers of thefirst symmetrical arrangement. A patterned adhesive layer 445 isprovided between the two paper layers 420 and 440, and defines a patternof closed cells 450 configured to expand when exposed to microwaveenergy. In one aspect, an insulating material 300 having two metallayers 410 and 430 according to the present invention generates moreheat and greater cell loft.

Referring to FIG. 20, yet another insulating microwave material 400 isshown. The material 400 may include a PET film layer 405, a metal layer410, an adhesive layer 415, and a paper layer 420. Additionally, thematerial 400 may include a clear PET film layer 425, an adhesive 435,and a paper layer 440. The layers are adhered or affixed by a patternedadhesive 445 defining a plurality of closed expandable cells 450.

Any of the insulating materials shown herein or contemplated hereby mayhave barrier properties that render the package suitable for storage ofa food item therein. Such insulating materials may include a layer ofbarrier film in addition to the other layers present, or may replace afilm layer previously described herein. Various exemplary barrier filmsthat may be suitable for use with the present invention are describedabove.

As stated above, any of such insulating materials may be used to formall or part of the various packages contemplated by the presentinvention. Thus, for example, FIG. 21 depicts the package of FIG. 1formed from an insulating material, FIG. 22 depicts the package of FIG.7 formed from an insulating material, and FIG. 23 depicts the package ofFIG. 8 formed from an insulating material, where each of FIGS. 1, 9, and10 illustrate the package upon exposure to microwave energy.

It should be understood that in any of the packages contemplated hereby,it may be necessary or desirable to configure the package to includeportions formed from a material other than an insulating material. Forexample, in one aspect, a package includes a food-supporting surfaceformed from a susceptor material, and a food-covering layer formed froman insulating microwave material. Such a package may be useful with fooditems that have a crust that is desirably browned and crisped, forexample, pizza. Likewise, the package may include portions, for example,proximate the edges or the opening that do not have an insulatingeffect. Thus, for example, the package may be designed to have the flap,zipper, or other closure mechanism attached or affixed to anon-insulating material. In yet another aspect, one or more portions ofthe package may be laminated or otherwise bonded or assembled orassembled so that portions of the package formed from an insulatingmaterial are rendered non-insulating. For example, an insulatingmaterial having expandable cells used to form a sleeve may be bondedaround all or a portion of the periphery so that the expandable cellscan no longer expand. As another example, the package may includeportions that include expanding cells that are positioned to maintainthe package in an upright position, a flattened position, or any otherconfiguration during cooking. Thus, advantageously, numerous packagesmay be tailored to various food items to optimize heating in themicrowave oven.

Use of any of the exemplary insulating materials, to package and/or cooka food item provides several benefits before, during, and after heatingin a microwave oven. First, the water vapor and air contained in theclosed cells provides insulation between the food item and the interiorsurfaces of the microwave oven. The base of a microwave oven, forexample, the glass tray found in most microwave ovens, acts as a largeheat sink, absorbing much of the heat generated by the susceptor film orwithin the food item itself. The vapor pockets in the cells formed bythe present invention may be used to insulate the food item andsusceptor film from the microwave oven surfaces and the vented air inthe microwave oven cavity, thereby increasing the amount of heat thatstays within or is transferred to the food item.

Second, the formation of the cells allows the material to conform moreclosely to the surface of the food item, placing the susceptor film ingreater proximity to the food item. This enhances the ability of thesusceptor film to brown and crisp the surface of the food item byconduction heating, in addition to some convection heating, of the fooditem.

Further, the insulating materials contemplated hereby may be desirableas a packaging material because it adds little bulk to the finishedpackage, yet is transformed into a bulk insulating material without anyconsumer preparation before cooking.

According to one aspect of the present invention, a plurality ofmicrowave cooking packages are provided in a nestled, stacked, folded,rolled, or other configuration. Thus, for example, a plurality ofpackages may be stacked in a face-to-face relation, then folded orrolled and placed in a bag, box, or other carton. The carton may includea portion that tears away using perforations, folds, tabs, or otherwise,to form an open portion through which the microwave cooking packages maybe removed or dispensed.

The user then may dispense or otherwise remove a cooking package fromthe bag or carton, and place a food item to be cooked into the interiorthereof. The package may be sealed by any of various mechanisms, forexample, those described above, and placed in the refrigerator, freezer,lunch bag, briefcase, or otherwise, for later use. For example, the fooditem may be placed in the refrigerator for later consumption by anotherfamily member, such as a spouse or child. When the user wants to consumethe food item, the packaged optionally is opened for venting (asdescribed above) and the package is placed in the microwave oven. Afterheating, the food item may be removed from the package if desired.Alternatively, the food item may be consumed while still in the package,and the package may gradually be pulled away from the food item toexpose it. If desired, the package may be provided with tear lines orperforations to aid in removal of the food item from the package.

The present invention is illustrated further by the following examples,which are not to be construed in any way as imposing limitations uponthe scope thereof. On the contrary, it is to be clearly understood thatresort may be had to various other aspects, modifications, andequivalents thereof which, after reading the description herein, may besuggested to one of ordinary skill in the art without departing from thespirit of the present invention or the scope of the appended claims.

EXAMPLE 1

The conductivity of various susceptor films was evaluated. Indium tinoxide coated (ITO) films were provided by Sheldahl Films (Northfield,Minn.) for evaluation, as indicated in Table 1. Each of the filmsincluded one or more layers of a proprietary clear hard coat (“CLHC”)material to protect the individual layers. The films were laminated onthe ITO side to 75 gauge DARTEK N-201 nylon 6,6 film using Rohm & HaasMor-Free 205A/C-66 adhesive applied in an amount of about 1.2 lb/ream. A48-gauge polyethylene terephthalate (PET) film was evaluated as acontrol material. The results are presented in Table 1.

TABLE 1 Sheldahl No. of Conductivity Resistivity Sample No. ConstructionSamples (mhos/sq) (ohms/sq) 1 140669 40 ohm/sq ITO 9 0.014 to 71.4 to38.4 2 mil PET 0.026 2 159512 250 ohm/sq ITO 4 0.0036 to 277.8 to SiOx0.0037 270.3 CLHC 7.5 mil PET CLHC 3 159980 50 ohm/sq ITO 9 0.0166 to60.2 to SiOx 0.0173 57.8 CLHC 7.5 mil PET CLHC 4 control 48 gauge PET 10.016 to 62.5 to 0.017 58.8

The results indicate that the ITO films form susceptor materials thatmay be useful to form packages of the present invention. The use of a7.5 mil PET film may be desirable for packaging applications thatrequire or benefit from some level of stiffness or rigidity. However, itwill be understood that ITO may be used to form susceptor materialshaving a lower basis weight and, therefore, less rigidity, as needed ordesired for flexible packaging applications.

EXAMPLE 2

The barrier properties of Samples 2 and 3 from Example 1, each includinga silicon oxide (SiOx) barrier layer, also were evaluated. OxygenTransmission Rate (OTR) was measured at 22.8° C. and 0% relativehumidity. Water Vapor Transmission Rate was measured at 37.8° C. and100% relative humidity. The results are presented in Table 2. Theresults indicate that a SiOx layer may be used successfully to prepare abarrier susceptor suitable for use with the present invention.

TABLE 2 Sheldahl No. of OTR WVTR Sample No. Construction Samples(cc/m²/day) (g/m²/day) 2 159512 250 ohm/sq 4 <0.0496 0.0841 ITO SiOxCLHC 7.5 mil PET CLHC 3 159980 50 ohm/sq ITO 9 <0.0496 0.0143 SiOx CLHC7.5 mil PET CLHC

Accordingly, it will be readily understood by those persons skilled inthe art that, in view of the above detailed description of theinvention, the present invention is susceptible of broad utility andapplication. Many adaptations of the present invention other than thoseherein described, as well as many variations, modifications, andequivalent arrangements will be apparent from or reasonably suggested bythe present invention and the above detailed description thereof,without departing from the substance or scope of the present invention.

While the present invention is described herein in detail in relation tospecific aspects, it is to be understood that this detailed descriptionis only illustrative and exemplary of the present invention and is mademerely for purposes of providing a full and enabling disclosure of thepresent invention. The detailed description set forth herein is notintended nor is to be construed to limit the present invention orotherwise to exclude any such other embodiments, adaptations,variations, modifications, and equivalent arrangements of the presentinvention, the present invention being limited solely by the claimsappended hereto and the equivalents thereof.

1. A package for heating, browning, and/or crisping a food item in amicrowave oven, comprising: a pair of panels adjoined in an opposed,facing relationship to define a cavity and an open end, wherein thepanels are formed at least partially from a microwave energy interactiveinsulating material including a microwave energy interactive materialsupported on a first polymer film layer, a moisture-containing layerjoined to the microwave energy interactive material, and a secondpolymer film layer joined to the moisture-containing layer in apredetermined pattern, thereby forming a plurality of closed cellsbetween the moisture-containing layer and the second polymer film layer;and a closure mechanism proximate the open end, wherein the closuremechanism is selected from the group consisting of a zipper and aslider.
 2. The package of claim 1, wherein the microwave energyinteractive material comprises a layer of metal sufficiently thin toconvert at least a portion of impinging microwave energy to thermalenergy.
 3. The package of claim 1, wherein the moisture-containing layeris selected from the group consisting of paper, paperboard, and anycombination thereof.
 4. The package of claim 1, wherein at least one ofthe first polymer film and the second polymer film comprisespolyethylene terephthalate.
 5. The package of claim 1, wherein thesecond polymer film comprises biaxially-oriented polyethyleneterephthalate.
 6. The package of claim 1, wherein the second polymerfilm comprises amorphous polyethylene terephthalate.
 7. The package ofclaim 1, further comprising a vent adapted to allow the release ofmoisture from the package.
 8. The package of claim 1, wherein the closedcells are adapted to inflate in response to microwave energy.
 9. Apackage for heating, browning, and/or crisping a food item in amicrowave oven, comprising: a first panel and a second panel adjoined inan opposed, facing relationship to define a cavity and an opening,wherein the first panel and the second panel are each formed at leastpartially from a microwave energy interactive insulating materialincluding a microwave energy interactive material supported on a firstpolymer film layer, a moisture-containing layer joined to the microwaveenergy interactive material, and a second polymer film layer joined tothe moisture-containing layer in a predetermined pattern, therebyforming a plurality of closed cells between the moisture-containinglayer and the second polymer film layer; and a closure mechanismproximate the opening, wherein the closure mechanism comprises a tabthat communicates with a corresponding slot in the first panel.
 10. Thepackage of claim 9, wherein the tab extends from a flap joined to thesecond panel proximate the opening.
 11. The package of claim 10, whereinthe flap is adapted to be folded over the opening.
 12. The package ofclaim 9, wherein the microwave energy interactive material comprises alayer of metal sufficiently thin to convert at least a portion ofimpinging microwave energy to thermal energy.
 13. The package of claim9, wherein the moisture-containing layer is selected from the groupconsisting of paper, paperboard, and any combination thereof.
 14. Thepackage of claim 9, wherein at least one of the first polymer film andthe second polymer film comprises polyethylene terephthalate.
 15. Thepackage of claim 9, wherein the second polymer film comprisesbiaxially-oriented polyethylene terephthalate.
 16. The package of claim9, wherein the second polymer film comprises amorphous polyethyleneterephthalate.
 17. The package of claim 9, further comprising a ventadapted to allow the release of moisture from the package.
 18. Thepackage of claim 9, wherein the closed cells are adapted to inflate inresponse to microwave energy.
 19. A package for heating, browning,and/or crisping a food item in a microwave oven, comprising: a pair ofpanels adjoined in an opposed, facing relationship to define a cavity,an interior surface, and an open end; and an adhesive material overlyingthe interior surface of at least one of the panels proximate the openend, wherein the panels are formed at least partially from a microwaveenergy interactive insulating material including a microwave energyinteractive material supported on a first polymer film layer, amoisture-containing layer joined to the microwave energy interactivematerial, and a second polymer film layer joined to themoisture-containing layer in a predetermined pattern, thereby forming aplurality of closed cells between the moisture-containing layer and thesecond polymer film layer, wherein the closed cells are adapted toinflate in response to microwave energy.
 20. The package of claim 19,wherein the microwave energy interactive material comprises a layer ofmetal sufficiently thin to convert at least a portion of impingingmicrowave energy to thermal energy.
 21. The package of claim 19, whereinthe moisture-containing layer is selected from the group consisting ofpaper, paperboard, and any combination thereof.
 22. The package of claim19, wherein at least one of the first polymer film and the secondpolymer film comprises polyethylene terephthalate.
 23. The package ofclaim 19, wherein the second polymer film comprises biaxially-orientedpolyethylene terephthalate.
 24. The package of claim 19, wherein thesecond polymer film comprises amorphous polyethylene terephthalate. 25.The package of claim 19, further comprising a vent adapted to allow therelease of moisture from the package.